I came across these a couple months ago. I ordered a few of them and they seem to work really well with my triggers on my standard LPK's. If you get 10 to split with your friends, they're $10 each, $3 shipping.
http://www.ar15triggeradjusters.com/
They're not the Carpenter 158 bolts, but good for a cheap build or spare.
http://palmettostatearmory.com/index.php/featured/p-tac-ar-15-8620-bolt-carrier-group.html
I used to tap the grip hole all the way through on in-house trigger jobs and add a set screw. Problem is that tapping does loosen the grip screw hole by removing the anodizing and some more aluminum. Also the original grip screw may require being shortened some or you can't tighten the grip...